This invention relates to communications antenna arrays, and more particularly relates to such arrays used to communicate data over multi-octave bandwidths.
The current state of the antenna art is unable to provide an array element with the wide scanning and the multi-octave bandwidth needed for some applications. The multi-octave bandwidth typically needed is greater than 4 to 1. The current state of the art includes printed notches such as those described in xe2x80x9cFD-TD Analysis of Vivaldi Flared Horn Antennas and Arraysxe2x80x9d by E. Thiele, IEEE Transactions On Antennas And Propagation, Vol. 42, No. 5, May, 1994. Radio waves are guided by the printed notches. The printed notches have electric insulating material at their center. Thus, the central portion of the radio waves is guided by insulating material. The applicants believe that the exposed insulating material contributes to the deficiencies of such printed notches.
The current state of the art also includes a crossed ridge antenna developed at TRW such as shown in FIG. 1. In the TRW design, the crossed ridges are arranged in intersecting pairs. The applicants believe that such intersection contributes to problems encountered in some applications.
Both the printed notch and crossed ridge antennas have been found to support resonant modes, which seriously degrade scan performance at one or more frequencies in a multi-octave band. This phenomenon is known as scan blindness. These degradations render the array element unusable in many applications. This invention addresses the problem of scan blindness and provides a solution.
The preferred embodiment includes an antenna array comprising a plurality of antenna elements. The elements cooperate to communicate radio frequency waves. Each element preferably comprises an element structure having a gap arranged to couple radio frequency energy. The element structure defines a gap plane bisecting the gap. A first tapered surface and a second tapered surface extend from the element structure to a mouth and are arranged to couple the radio frequency energy through the mouth. The first and second tapered surfaces define a first section of a first tapered-surface plane perpendicular to the gap plane and bisecting the first and second tapered surfaces. A first mid portion of the first tapered surface and a second mid portion of the second tapered surface intersect the first tapered-surface plane. The first section has a boundary defined at the periphery of the mouth, and the other elements in the array are arranged such that no other tapered-surface plane of another pair of tapered surfaces in the array intersects the first section. A conductive surface covers at least the mid portions of the tapered surfaces.
According to another embodiment, an antenna array is provided with a plurality of antenna elements capable of coupling a plurality of radio frequency waves. In such an environment, the waves preferably are communicated by guiding at least the central portion of opposed edges of the waves with a conductive material and by isolating the waves from each other.
According to another embodiment of the invention, at least a majority of the elements in the antenna array comprise an element structure having a gap arranged to couple radio frequency energy. The element structure defines a gap plane bisecting the gap. A surface having a predetermined thickness parallel to the gap plane extends from the element structure to a mouth defining a mouth length. The surface is arranged to couple the radio frequency energy through the mouth. The ratio of the predetermined thickness to the mouth length is such that there would be no substantial increase in the high frequency limit of the array if the ratio were increased.
According to another embodiment of the invention, at least a majority of the elements in the antenna array comprise an element structure having a gap arranged to couple radio frequency energy. The element structure defines a gap plane bisecting the gap. A surface having a predetermined thickness parallel to the gap plane extends from the element structure to a mouth defining a mouth length. In such an antenna, the antenna elements preferably are tuned by increasing the ratio of the predetermined thickness to the mouth length until there is no substantial increase in the high frequency limit of the array.